Lovecraft might have liked this new paper by Frank and colleagues, since he though squid-like beings could dream...

In his house at R’lyeh, dead Cthulu waits dreaming.

Sleep is a surprisingly thorny behaviour to explain. Why should an animal stop attending the world around them (or, to put it in human terms, losing consciousness), leaving itself vulnerable to how knows how many shocks and threats?

Research on human sleep has defined and driven sleep research. The question of invertebrate sleep, for example, was very slow to develop because of the problems in comparing invertebrate neurophysiology to vertebrate neurophysiology. Research on human sleep had been revolutionized by the Hans Berger’s introduction of electroencephalography (EEG), which allowed us to see the differences in brainwaves during sleep. EEGs defined sleep research so much that one researcher I know was told that she could not say an invertebrate was sleeping because there were no records of brain waves, regardless of what the behaviour was.

Cephalopods are potentially very interesting subjects for sleep research because of their brainwaves. When you try to record brainwaves from most invertebrates, you get very spiky recordings rather than waves. Cephalopods, and particularly octopuses, have brain waves that are more vertebrate like: wavy, not spiky (Ted Bullock wrote about this quote a bit). So for those who define sleep by changes in brain wave activity, cephalopods may offer more points of comparison.

This new paper by Frank and company doesn’t have brainwaves, but could be an important first step in developing methods to study sleep in cephs. They do two things here.

First, they document that cuttlefish go through periods of behavioural sleep: prolonged inactivity. They call this an experiment, but there isn’t any manipulation, so it’s really just a study. They do document some intermittent behaviours that they argue are analogous to rapid eye movement (REM) sleep in mammals, though I don’t buy that at all.

The second experiment is much more interesting. I’m sure everyone has had the experience when you don’t get enough sleep. When you’ve been deprived of sleep, the next time you do sleep, you sleep more than normal. That “rebound” is evidence that the inactive state is sleep and not just inactivity.

So Frank and company sleep deprived their cuttlefish. Now, sleep depriving an animal is a very tricky business. How do you stop a cuttlefish from sleeping?

This was one of those rare times I was glad I read the methods section.

A vertically-facing LCD computer monitor was positioned beneath the bottom of the tank. Hans Zimmer’s “King Arthur” film score (2004) was played (Microsoft’s Window Media Player) and the visualizer option was used to project random shapes on the screen. Angled mirrors placed around the sides of the tank reflected the screen image all around the cuttlefish to ensure constant, gently moving visual stimulation.

That’s... oddly specific.

Regardless of their choice of film scores, Frank and company did indeed find that after being prevented from “sleep,” their cuttlefish did indeed sleep more when next given the chance.

This is a very cool and promising start on sleep research in cephs. But I’ll tell the authors this for free: if you want to push this further and catch the attention of mainstream sleep researchers, you’re going to have to record brain activity. It will be maddeningly hard, but if you can get those data, that’s when things will start to get fun.

Humm, I don't know Starvos, the videos definitely remind me of a dog running in its sleep kind of behavior (particularly the first, S1 video). I have to admit to rolling my eyes a bit () when sleep is challenged in octos because it is quite clear that they go inactive for periods and can be easily startled "awake". The diurnals are particularly clear about sleeping and becoming "grumpy" if deprived (I had to do my laundry during the day with one animal because he became very nervous with the vibration from the dryer in the room adjourning his tank, would pace and then be sluggish and unresponsive the next day). Dreaming can certainly be challenged but I have a really hard time with denying they sleep.

D, we agree and I am 'convinced' that cephs do show sleep-like activity. Now, the blogger here raises some important questions for future research on this behavior; if we are to convince sleep researchers that sleep behavior does exist in cephs, then there are specific dependent measures to be taken into account. In this case, chromatophore activity, motor and oculomotor responses are not sufficient to 'prove' REM-sleep stage. (However, there is certainly enough evidence that 'something' really interesting takes place and begs for further investigation.)

It's going to be difficult to get an encephalograph on sepia (or any other ceph for that matter), to measure neural activity and characterize stages of sleep, but the point is not about a necessity to useone specific method, rather than coming up with specific measurements, recording brain waves in this case. If brain waves are recorded and can be used to characterize sleep behavior and a REM-like stage, then chromatophore activity, oculomotor responses and such will be gravy.

I had the luck to attend a talk for this specific study recently and discuss with one of the authors afterwards the specific thresholds they plan to measure. It is still an early stage study definitely, but the behavior is there. Personally, I'm really glad for this study. It lays foundations for the field to grow in new directions.

Stavros,
TONMO Member, Peter Godfrey-Smith added some thoughts to this as well as some interesting conjecture about dreaming in his blog, The Giant Cuttlefish. I am not sure if he borrowed the title idea or the topic lends itself to the question but his entry is titled, "Do cuttlefish Dream of Electric Eels"